Turbo compressor and turbo refrigerator provided with same

ABSTRACT

To realize a reduction in cost and extension of the lifespan of a auxiliary bearing which is disposed adjacent to a non-contact bearing supporting a rotor shaft of a centrifugal compressor. A centrifugal compressor ( 2 ) includes: a rotor shaft ( 15 ); an electric motor ( 14 ) provided at an intermediate portion of the rotor shaft ( 15 ) in a coaxial manner with the rotor shaft ( 15 ), the electric motor ( 14 ) being configured to rotationally drive the rotor shaft ( 15 ); an impeller ( 16 ) fixed to one end of the rotor shaft ( 15 ) and forming a refrigerant compressing unit ( 7 ) which compresses a refrigerant; main bearings ( 18   a   , 18   b ) formed of non-contact bearings pivotally supporting the rotor shaft ( 15 ) at a portion between the electric motor ( 14 ) and the impeller ( 16 ), and at another end of the rotor shaft ( 15 ); auxiliary bearings ( 19   a   , 19   b ) disposed adjacent to the main bearings ( 18   a   , 18   b ), the auxiliary bearings being configured to pivotally support the rotor shaft ( 15 ) in place of the main bearings ( 18   a   , 18   b ) in a state where functioning of the main bearings ( 18   a   , 18   b ) stops; and a lubricating refrigerant supply unit ( 25 ) configured to supply the refrigerant as a lubricant to an inside of the auxiliary bearings ( 19   a   , 19   b ) in the state where the functioning of the main bearings ( 18   a   , 18   b ) stops.

TECHNICAL FIELD

The present invention relates to a turbo compressor, and a centrifugal chiller provided with the same.

BACKGROUND ART

As well known, a centrifugal chiller, such as one used as a heat source for district heating and cooling, includes a centrifugal turbine type centrifugal compressor which is driven by an electric motor. As disclosed in Patent Literature 1, there is known a centrifugal compressor where non-contact bearings, such as magnetic bearings or gas bearings (air bearings), are used as bearings for a rotor shaft so that the bearings have no rotational resistance and, at the same time, no lubrication of the bearings is required. The non-contact bearings support the rotor shaft in a floating state with respect to the bearings. Accordingly, rotational resistance of the bearings can be made extremely small.

In this case, auxiliary bearings (touchdown bearings) are provided, and the auxiliary bearings support the rotor shaft in place of the non-contact bearings when power supply cuts off due to power failure or the like so that the functioning of the non-contact bearings stops. Rolling bearings are used for the auxiliary bearings. A gap in a radial direction of the auxiliary bearing is set smaller than that of the non-contact bearing. Accordingly, when power supply cuts off, the rotor shaft is supported (touched down) by the auxiliary bearings prior to contacting with the non-contact bearings. Therefore, damage to the non-contact bearings can be prevented.

CITATION LIST Patent Literature

-   [PTL 1] Japanese Unexamined Patent Application, Publication No.     2002-218708

SUMMARY OF INVENTION Technical Problem

Rolling bearings are generally adopted for auxiliary bearings. However, non-contact bearings require no lubrication or no cooling so that a lubricant oil system is not provided. Accordingly, the auxiliary bearings, formed of the rolling bearings, are subject to perform grease lubrication or no lubrication in many cases.

For this reason, there has been a problem that a lifespan of the auxiliary bearing is short, or the number of touchdowns is limited. For preventing such a problem, it is necessary to adopt special steel as a material for forming the auxiliary bearings, or to apply special surface treatment to an inner and outer races and a rolling element, thus making a bearing system expensive.

The present invention has been made under such circumstances, and it is an object of the present invention to provide a centrifugal compressor which can realize a reduction in cost and extension of the lifespan of a auxiliary bearing disposed adjacent to a non-contact bearing supporting a rotor shaft, and to provide a centrifugal chiller provided with the centrifugal compressor.

Solution to Problem

To overcome the above-mentioned problem, the present invention adopts the following means.

A centrifugal compressor according to a first aspect of the present invention includes: a rotor shaft; an electric motor provided at an intermediate portion of the rotor shaft in a coaxial manner with the rotor shaft, the electric motor being configured to rotationally drive the rotor shaft; an impeller fixed to one end of the rotor shaft and forming a refrigerant compressing unit which compresses a refrigerant; a non-contact bearing configured to pivotally support the rotor shaft at a portion between the electric motor and the impeller, and a non-contact bearing configured to pivotally support the rotor shaft at another end of the rotor shaft; an auxiliary bearing disposed adjacent to the non-contact bearing, the auxiliary bearing being configured to pivotally support the rotor shaft in place of the non-contact bearing in a state where functioning of the non-contact bearing stops; and a lubricating refrigerant supply unit configured to supply the refrigerant as a lubricant to an inside of the auxiliary bearing in the state where the functioning of the non-contact bearing stops.

According to the centrifugal compressor having the above-mentioned configuration, when power supply cuts off due to power failure or the like so that the functioning of the non-contact bearings stops, the auxiliary bearing supports the rotor shaft in place of the non-contact bearing and, at the same time, a refrigerant is supplied as a lubricant to the inside of the auxiliary bearing by the lubricating refrigerant supply unit. Accordingly, a lubrication state of the auxiliary bearing can be improved, and a conventional bearing can be used without using a special expensive bearing, thus realizing a reduction in cost and extension of the lifespan of the auxiliary bearing.

In the above-mentioned configuration, the lubricating refrigerant supply unit may include: a liquid refrigerant storage unit in which the refrigerant in a liquid phase is stored; a liquid refrigerant supply passage configured to connect the auxiliary bearing and the liquid refrigerant storage unit with each other; and a solenoid valve connected to the liquid refrigerant supply passage, the solenoid valve being configured to close in an energized state.

With the above-mentioned configuration, the solenoid valve, which closes when in an energized state, opens when power supply cuts off. Accordingly, the refrigerant in a liquid phase stored in the liquid refrigerant storage unit is supplied to the auxiliary bearing through the liquid refrigerant supply passage. According to this configuration, without providing a control unit, a refrigerant can be supplied to the auxiliary bearing by opening the solenoid valve when power supply cuts off, thus realizing a reduction in cost of the bearing system.

In the above-mentioned configuration, the liquid refrigerant storage unit may be formed of a bottom portion of a condenser where the refrigerant compressed by the refrigerant compressing unit is to be condensed. A compressed and condensed refrigerant in a liquid phase is stored in a bottom portion of the condenser, and the pressure of this refrigerant in a liquid phase is higher than an ambient pressure of the auxiliary bearings. Accordingly, simultaneously with the opening of the solenoid valve, the refrigerant is rapidly supplied to the auxiliary bearings due to a pressure difference. Therefore, when power supply cuts off, a refrigerant can be quickly supplied to the auxiliary bearings so as to lubricate the auxiliary bearings, thus realizing extension of the lifespan of the auxiliary bearings.

In the above-mentioned configuration, the liquid refrigerant storage unit may be formed of a liquid refrigerant jacket for cooling the electric motor, the liquid refrigerant jacket being provided to a casing which houses the electric motor. The liquid refrigerant jacket is positioned in the vicinity of the auxiliary bearings, and a compressed and condensed refrigerant in a liquid phase circulates through the liquid refrigerant jacket. Accordingly, simultaneously with the opening of the solenoid valve when power supply cuts off, the refrigerant in the liquid refrigerant jacket can be easily supplied to the auxiliary bearings due to a pressure difference or gravity. According to this configuration, it is unnecessary to connect the centrifugal compressor and peripheral equipment by the liquid refrigerant supply passage and hence, the bearing system can be simplified.

In the above-mentioned configuration, the liquid refrigerant storage unit may be formed of a pressure applying container which stores the refrigerant in a liquid phase while applying a pressure higher than an ambient pressure of the auxiliary bearing. With such a configuration, simultaneously with the opening of the solenoid valve when power supply cuts off, the refrigerant in the pressure applying container is supplied to the auxiliary bearings due to a pressure difference. According to this configuration, it is unnecessary to provide a system which extracts a refrigerant compressed by a centrifugal compressor and hence, the bearing system can be simplified. Further, irrespective of the operation state of the chiller, a lubricating refrigerant supply pressure can be maintained at a value equal to or more than a required specified value and hence, a lubricating refrigerant can be supplied with certainty.

In the above-mentioned configuration, the auxiliary bearing may be formed of a rolling bearing, and a ceramic material may be adopted as a material for forming at least one of an outer race, an inner race, and a rolling element of the auxiliary bearing. The ceramic material has a small amount of thermal expansion so that an amount of size variation of the bearing gap can be made small when the temperature of the auxiliary bearing varies. Accordingly, a fluid having low viscosity, such as a refrigerant, can favorably lubricate the auxiliary bearings.

In the above-mentioned configuration, the auxiliary bearing may be formed of a rolling bearing, and a material which allows formation of a lubricating film with lubrication due to a low viscosity fluid may be adopted as a material for forming at least one of an outer race, an inner race, and a rolling element of the auxiliary bearing. With such a configuration, a fluid having low viscosity, such as a refrigerant, can favorably lubricate the auxiliary bearings.

In the above-mentioned configuration, the auxiliary bearing may be formed of a rolling bearing, and at least one of an outer race, an inner race, and a rolling element of the auxiliary bearing may be coated with diamond-like carbon. Diamond-like carbon allows the formation of a lubricating film with lubrication due to a low viscosity fluid and hence, a fluid having low viscosity, such as a refrigerant, can favorably lubricate the auxiliary bearings.

A centrifugal chiller according to a second aspect of the present invention includes: the centrifugal compressor described in any one of the above-mentioned configurations; a condenser configured to condense the refrigerant compressed by the centrifugal compressor; and an evaporator configured to evaporate the refrigerant condensed. With such a configuration, the above-mentioned respective manner of operations and advantageous effects can be acquired.

Advantageous Effects of Invention

As described above, according to the turbo compressor and the centrifugal chiller provided with the same of the present invention, it is possible to realize both of a reduction in cost and extension of the lifespan of a auxiliary bearing disposed adjacent to the non-contact bearing supporting the rotor shaft of the centrifugal compressor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an overall view of a centrifugal chiller showing a first embodiment of the present invention.

FIG. 2 is an enlarged longitudinal cross-sectional view of a centrifugal compressor shown in FIG. 1.

FIG. 3 is an enlarged longitudinal cross-sectional view of a centrifugal compressor showing a second embodiment of the present invention.

FIG. 4 is an overall view of a centrifugal chiller showing a third embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a plurality of embodiments of the present invention are described with reference to drawings.

First Embodiment

FIG. 1 is an overall view of a centrifugal chiller showing a first embodiment of the present invention. The centrifugal chiller 1 is configured to include: a centrifugal compressor 2 which compresses a refrigerant; a condenser 3; an expansion valve 4; and an evaporator 5. A refrigerant compressing unit 7 of the centrifugal compressor 2 and the condenser 3 are connected with each other by a discharge pipe 8. The condenser 3 and the evaporator 5 are connected with each other by a refrigerant pipe 9. The evaporator 5 and the centrifugal compressor 2 (refrigerant compressing unit 7) are connected with each other by a suction pipe 10. The expansion valve 4 is connected to the refrigerant pipe 9.

In this centrifugal chiller 1, a refrigerant compressed by the centrifugal compressor 2 (refrigerant compressing unit 7) is fed to the condenser 3 through the discharge pipe 8, and is subjected to heat exchange with cooling water in the condenser 3 and hence, heat of condensation is cooled so that the refrigerant is condensed. The cooling water heated in the condenser 3 is utilized for air heating conditioning or the like.

The refrigerant condensed in the condenser 3 passes through the expansion valve 4 provided to the refrigerant pipe 9, thus being adiabatically expanded, and fed to the evaporator 5. In the inside of the evaporator 5, the refrigerant, which is adiabatically expanded in the expansion valve 4 thus having a low temperature, is subjected to heat exchange with water. Chilled water cooled in the evaporator 5 is utilized for air cooling conditioning or as industrial cooling water. The refrigerant which is vaporized due to heat exchange with cooling water is sucked into the centrifugal compressor 2 (refrigerant compressing unit 7) again through the suction pipe 10, and is compressed. Hereinafter, this cycle is repeated.

As also shown in FIG. 2, the centrifugal compressor 2 is configured to include: a casing 13 forming an outer shell of the centrifugal compressor 2; an electric motor 14; a rotor shaft 15; impellers 16 forming the refrigerant compressing unit 7; a pair of main bearings 18 a, 18 b; a pair of auxiliary bearings 19 a, 19 b disposed adjacent to these main bearings 18 a, 18 b; and thrust bearings 20 a, 20 b. The inside of the casing 13 is divided into an electric motor chamber 13A and a compression chamber 13B by a partition wall 13 a. The electric motor 14 is housed in the electric motor chamber 13A, and the refrigerant compressing unit 7 (impellers 16) is housed in the compression chamber 13B.

The electric motor 14 is configured to include a stator 14 a and a rotor 14 b. The stator 14 a is fixed to the casing 13 side. The rotor 14 b is fixed to the rotor shaft 15, and rotates in the stator 14 a. One end of the rotor shaft 15 penetrates the partition wall 13 a and is inserted into the compression chamber 13B. The impellers 16 are provided to the inserted portion such that the impellers 16 rotate integrally with the rotor shaft 15, thus forming the refrigerant compressing unit 7.

One main bearing (18 a) out of the pair of main bearings 18 a, 18 b pivotally supports a portion of the rotor shaft 15 between the electric motor 14 and the impeller 16, and the other main bearing (18 b) pivotally supports the other end (an end portion on the side opposite to the impellers 16) of the rotor shaft 15. For these main bearings 18 a, 18 b, known non-contact bearings, such as magnetic bearings or gas bearings (air bearings) are used. With such a configuration, rotational resistance can be reduced and no lubrication is required.

The pair of auxiliary bearings 19 a, 19 b, which are disposed adjacent to the main bearings 18 a, 18 b, are formed of rolling bearings. The auxiliary bearings 19 a, 19 b pivotally support the rotor shaft 15 in place of the main bearings 18 a, 18 b in a state where the functioning of the main bearings 18 a, 18 b stops when power supply cuts off, such as when power failure occurs. That is, the auxiliary bearings 19 a, 19 b are so-called touchdown bearings. The bearing gap of the auxiliary bearings 19 a, 19 b is designed to be sufficiently smaller than the bearing gap of the main bearings 18 a, 18 b. For example, the bearing gap of the auxiliary bearings 19 a, 19 b is designed to be approximately half of the bearing gap of the main bearings 18 a, 18 b. Accordingly, even in the case where the functioning of the main bearings 18 a, 18 b stops so that the auxiliary bearings 19 a, 19 b support the rotor shaft 15, the bearing gaps of the main bearings 18 a, 18 b remain and hence, damage to the main bearings 18 a, 18 b can be avoided.

The thrust bearings 20 a, 20 b are provided on opposite sides of a disk-shaped thrust plate 15 a, and the thrust plate 15 a is disposed at a distal end of the rotor shaft 15 on the other end side. The thrust bearings 20 a, 20 b restricts the movement of the rotor shaft 15 in the axial direction. In the same manner as the main bearings 18 a, 18 b, the thrust bearings 20 a, 20 b are also formed of non-contact bearings.

As shown in FIG. 1 and FIG. 2, the centrifugal compressor 2 is provided with a lubricating refrigerant supply unit 25. The lubricating refrigerant supply unit 25 supplies a liquid refrigerant as a lubricant to the inside of the auxiliary bearings 19 a, 19 b formed of rolling bearings which support the rotor shaft 15 in place of the main bearings 18 a, 18 b as described above when power supply cuts off due to power failure or the like so that the functioning of the main bearings 18 a, 18 b, formed of non-contact bearings, stops. The lubricating refrigerant supply unit 25 includes: a liquid refrigerant storage unit 26 in which a refrigerant R in a liquid phase is stored; a liquid refrigerant supply passage 27 configured to connect the liquid refrigerant storage unit 26 and the auxiliary bearings 19 a, 19 b with each other; and a solenoid valve 28 connected to the liquid refrigerant supply passage 27.

In this embodiment, a bottom portion of the condenser 3 is utilized as the liquid refrigerant storage unit 26. A compressed and condensed refrigerant R in a liquid phase is always stored in the bottom portion of the condenser 3, and one end of the liquid refrigerant supply passage 27 is connected to the bottom portion at a position lower than the liquid surface of the refrigerant R in a liquid phase. The other end of the liquid refrigerant supply passage 27 is branched into two branch passages 27 a, 27 b. One branch passage 27 a is connected to one auxiliary bearing 19 a, and the other branch passage 27 b is connected to the other auxiliary bearing 19 b. The solenoid valve 28 is connected to the liquid refrigerant supply passage 27 at a section forward of where the liquid refrigerant supply passage 27 is branched. The solenoid valve 28 closes when in an energized state. That is, the solenoid valve 28 is a normally-open solenoid valve.

With respect to the centrifugal chiller 1 and the centrifugal compressor 2 having the above-mentioned configuration, when power supply cuts off due to power failure or the like, the functioning of the main bearings 18 a, 18 b, formed of non-contact bearings, stops. Accordingly, the auxiliary bearings 19 a, 19 b support the rotor shaft 15 in place of the main bearings 18 a, 18 b. At the same time, the solenoid valve 28, which closes when in an energized state, opens due to cutoff of power supply.

A refrigerant R in a liquid phase is stored in the liquid refrigerant storage unit 26, which is disposed at the bottom portion of the condenser 3, and the pressure of the refrigerant R is higher than the ambient pressure of the auxiliary bearings 19 a, 19 b (an inner pressure of the casing 13). Accordingly, simultaneously with the opening of the solenoid valve 28, the refrigerant R is supplied to the auxiliary bearings 19 a, 19 b through the liquid refrigerant supply passage 27 (branch passages 27 a, 27 b) due to a pressure difference. Therefore, the refrigerant R in a liquid phase is supplied as a lubricant to the inside of the auxiliary bearings 19 a, 19 b so that the auxiliary bearings 19 a, 19 b are lubricated and cooled.

As described above, the centrifugal compressor 2 includes the lubricating refrigerant supply unit 25 which supplies a refrigerant R in a liquid phase as a lubricant to the inside of the auxiliary bearings 19 a, 19 b, which support the rotor shaft 15 in place of the main bearings 18 a, 18 b formed of non-contact bearings, in a state where the functioning of the main bearings 18 a, 18 b stops. Accordingly, a lubrication state of the auxiliary bearings 19 a, 19 b when power supply cuts off can be improved, and conventional bearings can be used without using special expensive bearings. Therefore, it is possible to realize both of a reduction in cost and extension of the lifespan of the auxiliary bearings 19 a, 19 b.

For the solenoid valve 28 which opens the liquid refrigerant supply passage 27 when power supply cuts off, a normally-open solenoid valve which closes when in an energized state is adopted. Accordingly, without providing a dedicated control unit, a refrigerant R can be supplied to the auxiliary bearings 19 a, 19 b by opening the solenoid valve 28 when power supply cuts off. Therefore, it is possible to realize a reduction in cost of a bearing system.

The liquid refrigerant storage unit 26 is a supply source of a refrigerant R in a liquid phase to be supplied as a lubricant to the inside of the auxiliary bearings 19 a, 19 b, and the liquid refrigerant storage unit 26 is formed of the bottom portion of the condenser 3. A compressed and condensed refrigerant R in a liquid phase is stored in the bottom portion of the condenser 3, and the pressure of the refrigerant R in a liquid phase is higher than the ambient pressure of the auxiliary bearings 19 a, 19 b. Accordingly, simultaneously with the opening of the solenoid valve 28, the refrigerant R is rapidly supplied to the auxiliary bearings 19 a, 19 b due to a pressure difference. Therefore, when power supply cuts off, the refrigerant R can be quickly supplied to the auxiliary bearings 19 a, 19 b so as to lubricate the auxiliary bearings 19 a, 19 b, thus realizing extension of the lifespan of the auxiliary bearings 19 a, 19 b.

A ceramic material may be adopted as a material for forming at least one of an outer race, an inner race, and a rolling element of the auxiliary bearings 19 a, 19 b, formed of rolling bearings. The ceramic material has a small amount of thermal expansion so that an amount of size variation of the bearing gap can be made small when the temperature of the auxiliary bearings 19 a, 19 b varies. Accordingly, a fluid having low viscosity, such as the refrigerant R in a liquid phase, can favorably lubricate the auxiliary bearings 19 a, 19 b.

Further, as a material for forming at least one of the outer race, the inner race, and the rolling element of the auxiliary bearings 19 a, 19 b, a material which easily allows the formation of a lubricating film with lubrication due to a low viscosity fluid may be adopted. Alternatively, the outer race, the inner race, or the rolling element may be coated with a material, such as diamond-like carbon. With such a configuration, a fluid having low viscosity, such as the refrigerant R in a liquid phase, can favorably lubricate the auxiliary bearings 19 a, 19 b.

Second Embodiment

FIG. 3 is an enlarged longitudinal cross-sectional view of a centrifugal compressor 2A showing a second embodiment of the present invention. The centrifugal compressor 2A differs from the centrifugal compressor 2 of the first embodiment with respect to a point that a liquid refrigerant jacket 31, which extends along the circumferential direction, is formed at an intermediate portion in the axial direction of a casing 13 for the centrifugal compressor 2A. The liquid refrigerant jacket 31 is originally configured to cool an electric motor 14 (stator 14 a), and a refrigerant R in a liquid phase which is compressed and condensed thus being cooled and having a low temperature circulates through the liquid refrigerant jacket 31. Other configurations are similar to corresponding configurations of the centrifugal compressor 2 of the first embodiment and hence, corresponding components are given the same characters, and repeated description is omitted.

Also in the centrifugal compressor 2A, when power supply cuts off due to power failure or the like so that the functioning of main bearings 18 a, 18 b, formed of non-contact bearings, stops, auxiliary bearings 19 a, 19 b support a rotor shaft 15 in place of the main bearings 18 a, 18 b. Further, the centrifugal compressor 2A is provided with a lubricating refrigerant supply unit 32 which supplies a refrigerant as a lubricant to the inside of the auxiliary bearings 19 a, 19 b. In this lubricating refrigerant supply unit 32, the liquid refrigerant jacket 31 is utilized as a liquid refrigerant storage unit 33 in which a refrigerant R in a liquid phase is stored.

Further, the lubricating refrigerant supply unit 32 includes: a pair of liquid refrigerant supply passages 34 a, 34 b, which connect the liquid refrigerant jacket 31 and the auxiliary bearings 19 a, 19 b with each other; and solenoid valves 35 a, 35 b which are respectively connected to the liquid refrigerant supply passages 34 a, 34 b. Each of the solenoid valves 35 a, 35 b is a normally-open solenoid valve which closes when in an energized state in the same manner as the solenoid valve 28 in the first embodiment.

In the centrifugal compressor 2A having the above-mentioned configuration, when power supply cuts off due to power failure or the like, the functioning of the main bearings 18 a, 18 b, formed of non-contact bearings, stops so that the auxiliary bearings 19 a, 19 b support the rotor shaft 15 in place of the main bearings 18 a, 18 b. At the same time, the solenoid valves 35 a, 35 b, which close in an energized state, open due to cutoff of power supply. Accordingly, a refrigerant R in a liquid phase stored in the liquid refrigerant jacket 31 is supplied to the auxiliary bearings 19 a, 19 b through the liquid refrigerant supply passages 34 a, 34 b due to a pressure difference or gravity. Therefore, the refrigerant R in a liquid phase is supplied as a lubricant to the inside of the auxiliary bearings 19 a, 19 b so that the auxiliary bearings 19 a, 19 b are lubricated and cooled.

In this centrifugal compressor 2A, the liquid refrigerant jacket 31 is utilized as the liquid refrigerant storage unit 33 of the lubricating refrigerant supply unit 32. The liquid refrigerant jacket 31 is positioned in the vicinity of the auxiliary bearings 19 a, 19 b, and a compressed and condensed refrigerant R in a liquid phase circulates through the liquid refrigerant jacket 31. Accordingly, simultaneously with the opening of the solenoid valves 35 a, 35 b when power supply cuts off, the refrigerant R in the liquid refrigerant jacket 31 can be easily supplied to the auxiliary bearings 19 a, 19 b. According to this configuration, it is unnecessary to connect the centrifugal compressor 2A and peripheral equipment by a refrigerant supply passage and hence, a bearing system can be simplified.

Third Embodiment

FIG. 4 is an overall view of a centrifugal chiller showing a third embodiment of the present invention. In this centrifugal chiller 1A, the configuration of the centrifugal compressor 2 per se is similar to the configuration of the centrifugal compressor in the first embodiment (see FIG. 1, FIG. 2) and hence, corresponding components are given the same characters, and repeated description is omitted.

The centrifugal chiller 1A is also provided with a lubricating refrigerant supply unit 40 which supplies a refrigerant R as a lubricant to the inside of auxiliary bearings 19 a, 19 b which support a rotor shaft 15 in place of main bearings 18 a, 18 b when power supply cuts off. The lubricating refrigerant supply unit 40 includes: a liquid refrigerant storage unit 41 in which a refrigerant R in a liquid phase is stored; a liquid refrigerant supply passage 27 which connects the liquid refrigerant storage unit 41 and the auxiliary bearings 19 a, 19 b with each other; and a solenoid valve 28 connected to the liquid refrigerant supply passage 27. In the same manner as the liquid refrigerant supply passage 27 in the first embodiment, the liquid refrigerant supply passage 27 in this embodiment is branched into branch passages 27 a, 27 b, and connected to the auxiliary bearings 19 a, 19 b. However, the liquid refrigerant supply passage 27 in this embodiment differs from the first embodiment with respect to a point that an end portion of the liquid refrigerant supply passage 27 on the upstream side is connected not to a condenser 3 but to the liquid refrigerant storage unit 41. In the same manner as the first embodiment, the solenoid valve 28 is a normally-open solenoid valve which closes when in an energized state.

For the liquid refrigerant storage unit 41, a pressure applying container 43 is used which stores a refrigerant R in a liquid phase while applying a pressure higher than an ambient pressure of the auxiliary bearings 19 a, 19 b to the refrigerant R. The pressure applying container 43 includes: a container body 44 having a cylindrical shape, for example; a piston 45 which is provided in the container body 44 in a slidable manner in the axial direction; and a spring 46 which biases the piston 45 to an end surface (an end surface on the lower side in this embodiment) of the container body 44 to which the liquid refrigerant supply passage 27 is connected. The refrigerant R in a liquid phase stored in the pressure applying container 43 (container body 44) is pressed by the spring 46 by way of the piston 45 so that a pressure higher than an ambient pressure of the auxiliary bearings 19 a, 19 b (an inner pressure of the casing 13) is applied to the refrigerant R.

In the centrifugal chiller 1A and the centrifugal compressor 2 having the above-mentioned configuration, when power supply cuts off due to power failure or the like, the functioning of the main bearings 18 a, 18 b, formed of non-contact bearings, stops so that the auxiliary bearings 19 a, 19 b support the rotor shaft 15 in place of the main bearings 18 a, 18 b. At the same time, the solenoid valve 28, which closes when in an energized state, opens due to cutoff of power supply.

The refrigerant R in a liquid phase is stored in the pressure applying container 43 forming the liquid refrigerant storage unit 41, and a pressure higher than the ambient pressure of the auxiliary bearings 19 a, 19 b is applied to the refrigerant R by a biasing force of the spring 46. Accordingly, the refrigerant R is supplied to the auxiliary bearings 19 a, 19 b through the liquid refrigerant supply passage 27 (branch passages 27 a, 27 b) due to a pressure difference simultaneously with the opening of the solenoid valve 28. Therefore, the refrigerant R in a liquid phase is supplied as a lubricant to the inside of the auxiliary bearings 19 a, 19 b so that the auxiliary bearings 19 a, 19 b are lubricated and cooled.

According to this configuration, it is unnecessary to provide a system which extracts a refrigerant compressed by the centrifugal compressor 2 and hence, a bearing system can be simplified. Further, irrespective of the operation state of the centrifugal chiller 1A, a liquid lubricating refrigerant supply pressure can be maintained at a value equal to or more than a required specified value and hence, a liquid lubricating refrigerant can be supplied with certainty. The structure of the pressure applying container 43 is not always limited to the above-mentioned configuration. For example, the weight of a weight may be applied to the piston 45 instead of the biasing force of the spring 46. Alternatively, the structure may be changed to a so-called accumulator structure where the inside of the pressure applying container 43 is divided into two parts in the axial direction by a rubber film, a nitrogen gas or the like is sealed in one chamber closed, and a refrigerant R is stored in the other chamber to which the refrigerant supply passage 27 is connected.

As has been described above, according to the centrifugal compressors 2, 2A and the centrifugal chillers 1, 1A provided with the centrifugal compressors 2, 2A of the above-mentioned each embodiment, when the functioning of the main bearings 18 a, 18 b, formed of non-contact bearings supporting the rotor shaft 15 of the centrifugal compressors 2, 2A, stops, a liquid refrigerant can be supplied as a lubricant to the auxiliary bearings 19 a, 19 b, which are disposed adjacent to the main bearings 18 a, 18 b. Accordingly, it is possible to realize a reduction in cost and extension of the lifespan of the auxiliary bearings 19 a, 19 b.

The present invention is not limited to the configurations of the above-mentioned respective embodiments, and changes and modifications may be suitably made. Embodiments obtained by making such changes or modifications also fall within the scope of the present invention. For example, the overall configuration or application of the centrifugal chillers 1, 1A and the configuration or the like of the centrifugal compressors 2, 2A described in the above-mentioned embodiment merely form one example, and modifications can be applied to the respective components.

REFERENCE SIGNS LIST

-   1, 1A centrifugal chiller -   2, 2A centrifugal compressor -   3 condenser -   5 evaporator -   7 refrigerant compressing unit -   13 casing -   14 electric motor -   15 rotor shaft -   16 impeller -   18 a, 18 b main bearing (non-contact bearing) -   19 a, 19 b auxiliary bearing -   25, 32, 40 lubricating refrigerant supply unit -   26, 33, 41 liquid refrigerant storage unit -   27, 34 a, 34 b liquid refrigerant supply passage -   28, 35 a, 35 b solenoid valve -   31 liquid refrigerant jacket -   43 pressure applying container -   R refrigerant 

1. A centrifugal compressor comprising: a rotor shaft; an electric motor provided at an intermediate portion of the rotor shaft in a coaxial manner with the rotor shaft, the electric motor being configured to rotationally drive the rotor shaft; an impeller fixed to one end of the rotor shaft and forming a refrigerant compressing unit which compresses a refrigerant; a non-contact bearing configured to pivotally support the rotor shaft at a portion between the electric motor and the impeller, and a non-contact bearing configured to pivotally support the rotor shaft at another end of the rotor shaft; an auxiliary bearing disposed adjacent to the non-contact bearing, the auxiliary bearing being configured to pivotally support the rotor shaft in place of the non-contact bearing in a state where functioning of the non-contact bearing stops; and a lubricating refrigerant supply unit configured to supply the liquid refrigerant as a lubricant to an inside of the auxiliary bearing in the state where the functioning of the non-contact bearing stops.
 2. The centrifugal compressor according to claim 1, wherein the lubricating refrigerant supply unit includes: a liquid refrigerant storage unit in which the refrigerant in a liquid phase is stored; a liquid refrigerant supply passage configured to connect the auxiliary bearing and the liquid refrigerant storage unit with each other; and a solenoid valve connected to the liquid refrigerant supply passage, the solenoid valve being configured to close in an energized state.
 3. The centrifugal compressor according to claim 2, wherein the liquid refrigerant storage unit is formed of a bottom portion of a condenser where the refrigerant compressed by the refrigerant compressing unit is to be condensed.
 4. The centrifugal compressor according to claim 2, wherein the liquid refrigerant storage unit is formed of a liquid refrigerant jacket for cooling the electric motor, the liquid refrigerant jacket being provided to a casing which houses the electric motor.
 5. The centrifugal compressor according to claim 2, wherein the liquid refrigerant storage unit is formed of a pressure applying container which stores the refrigerant in a liquid phase while applying a pressure higher than an ambient pressure of the auxiliary bearing.
 6. The centrifugal compressor according to claim 1, wherein the auxiliary bearing is formed of a rolling bearing, and a ceramic material is adopted as a material for forming at least one of an outer race, an inner race, and a rolling element of the auxiliary bearing.
 7. The centrifugal compressor according to claim 1, wherein the auxiliary bearing is formed of a rolling bearing, and at least one of an outer race, an inner race, and a rolling element of the auxiliary bearing is coated with a material which allows formation of a lubricating film with lubrication due to a low viscosity fluid.
 8. The centrifugal compressor according to claim 1, wherein the auxiliary bearing is formed of a rolling bearing, and at least one of an outer race, an inner race, and a rolling element of the auxiliary bearing is coated with diamond-like carbon.
 9. A centrifugal chiller comprising: the centrifugal compressor described in claim 1; a condenser configured to condense the refrigerant compressed by the centrifugal compressor; and an evaporator configured to evaporate the refrigerant condensed. 